1. Field of the Invention
The present invention relates to circuits for amplifying electrical signals, and in particular to a circuit for amplifying electrical signals in a device for transmitting frequency-modulated emitter coupled logic (ECL) broad-band signals by means of coaxial lines.
2. Description of the Prior Art
A circuit for selected through-connection or inhibition of broad-band width signals is disclosed in U.S. Pat. No. 4,274,112, the electronic switches therein being designed as logic elements in ECL technology. Frequency-modulated signals having a broad band width, particularly carriers modulated by video signals, are transmitted by means of these logic elements.
ECL signals may be attenuated by longer coaxial cables of, for example, 100 meters in length, such that a line receiver is required at the end of the cable, the line receiver amplifying the attenuated signals up to ECL level. If the signal pulse duty factor or the a.sub.k2 harmonic value is to be improved, or at least not permitted to deteriorate, a relatively involved circuitry is required or alternatively an undesirable operating point balance is necessary.
Generally, symmetrical cables having symmetrical line receivers are utilized for digital ECL transmission over longer distances. This is not practical, however, without further circuitry particularly in the case of rectangular FM transmission. Moreover, such line receivers are galvanically driven in push-pull mode, and produce no improvement of the signal pulse duty factor.